Method for the production of castings from alloys of metals and gases

ABSTRACT

Method of and apparatus for dissolving a gas in molten metal and casting the metal in that condition. During the casting process a reservoir with the melt and the mold for the casting are disposed in separate chambers, such chambers being subjected to the pressure of an atmosphere composed by the gas to be dissolved in the molten metal and some other gas which is inert to the metal, the gases being present in such proportion that the partial pressure of the gas to be dissolved in the chamber with the mold is higher than that in the chamber with the reservoir for the melt. Thus, the solubility of the gas, which depends upon its partial pressure, may be equal in the melt, as well as in the solidifying metal; the total gas pressure in both chambers may be chosen in accordance with the requirement of the casting process, so that the melt may be conveyed to the mold.

United States Patent Balevski et al. Mar. 21, 1972 54] METHOD FOR THEPRODUCTION OF 2,426,814 9/1947 Burkhardt ..l64/66 x CASTING'S FROMALLOYS 0 METALS 2,724,160 11/1955 Scheuer ..l64/55 AND GASES 2,745,7405/1956 Jackson et al ..l64/5S UX 3,196,501 7/1965 Balevsky et al.......l64/1l9 [72] Inventors: Angel Tontchev Balevski; Ivan Dirnov3,402,756 9/ 1968 Frehser et al. ..l64/55 Nikolov, both of Sofia,Bulgaria Primary Examiner.l. Spencer Overholser [73] Assignee: lnstltutp0 Metaloznanie i Technologlna Assistant Examinepdohn E Roethel MetameSofia Bulgaria Attorney-Arthur O. Klein [22] Filed: Oct. 2, 1969 [5 7]ABSTRACT [2]] Appl. No.: 863,153

Method of and apparatus for dissolvmg a gas In molten metal and castingthe metal in that condition. During the casting 8" Appllcamm Dataprocess a reservoir with the melt and the mold for the casting Oct 91968 Bulgaria ..107s5 are dispmd 861mm"a chambers, such chambers beingjected to the pressure of an atmosphere composed by the gas [52] U S Cl164/55 75/59 164/66 to be dissolved in the molten metal and some othergas which "7 1 19 164/259 is inert to the metal, the gases being presentin such proportion [51] m Cl B22d 27/20 that the partial pressure of thegas to be dissolved in the l 58] Fie'ld l 19 259 chamber with the moldis higher than that in the chamber with the reservoir for the melt.Thus, the solubility of the gas, which depends upon its partialpressure, may be equal in the melt, as well as in the solidifying metal;the total gas pressure in both [56] References cued chambers may bechosen in accordance with the requirement UNITED STATES PATENTS of thecasting process, so that the melt may be conveyed to the mold.-1,888,132 11/1932 Kinzel 164/66 2,069,205 2/1937 Arness ..75/59 X 4Claims, 2 Drawing Figures Patented March 21, 1972 2 Sheets-Sheet 1ATTORNEY INVENTORS I Patented March 21, 1972 3,650,313

2 Sheets-Sheet 2 FIG. 2

INVENTORS'.

Ivan 1). Mf/(alav ATTORNEY METHOD FOR THE PRODUCTION OF CASTINGS FROMALLOYS OF METALS AND GASES The invention relates to a method ofproduction of shaped castings from metals and metal alloys, whichcontain in solid state a dissolved or chemically bound gas, in such aquantity as to exert an advantageous influence on the physical, chemicalor other properties of the material obtained, as well as to an apparatusfor the realization of the method. It is known, that gases whencontained as a solid solution or chemically bound components in thestructure of metals, have an extremely favorable effect on theirproperties. Nitrogen, as a typical example, induces in a number ofiron-based alloys the formation of structures with improved or newproperties. it is known on the other hand, that metals can dissolve,when in liquid state substantial gas quantities, but this capacity isgreatly reduced when the metal is in solid state. This peculiarityresults in very unpleasant effects in foundry practice: the gasesdissolved in the molten metal separate during its solidification,forming blowholes and other breaks in the structure. Therefore specialmeasures are required to prevent the gases from dissolving in the melt,or to lead off these gases before the solidification of the metal takesplace, e.g., by using vacuum.

It is possible to carry out the casting process in an autoclave at anincreased pressure of a gas whose dissolution is desirable. It isessential in this case that the pressure of the gas to be dissolvedshould be even higher during the solidification of the casting in orderto prevent the separation of the gas dissolved, as a result of its lowersolubility in the metal in solid state, corresponding to thecrystallization temperature. The obtaining of metal-gas alloys in anautoclave is a method that cannot be applied in the routine productionof shaped castings from this type of alloys, since they would be tooexpensive; therefore this method is of importance for laboratorypurposes only. The reason for this is the fact that in autoclave castingthe molten metal and the casting are disposed simultaneously in theautoclave space. If a high pressure of the gas to be dissolved isproduced inside, this will increase its concentration in the melt, andthe said gas will separate in the form of blowholes when the castingsolidifies.

This can be avoided if the pressure is abruptly increased during thecrystallization process. Thus the desired alloy can be obtained, but themelt is saturated with still more gas, this being undesirable andrequires a pressure reduction and degassing of the melt. For thesereasons, it is not possible in an autoclave apparatus to work with areservoir for molten metal, containing a larger quantity than requiredfor one casting, which makes such method more expensive.

The object of the present invention is to overcome the existingdifficulties in obtaining highly efficient alloys from metal and gasesby using a method which eliminates all the disadvantages mentioned,i.e., a method permitting the obtaining by comparatively simple meanscastings from such alloys in moulds, whereby the molten metal is treatedwith the gas to be dissolved in a separate reservoir, which is largercompared to the weight of the casting.

According to the present invention this problem is solved in such a waythat during the casting process the reservoir with the melt and themould are disposed in separate chambers, and are subjected to thepressure of an atmosphere composed by the gas to be dissolved, and someother gas which is inert to the metal, in such proportion, that thepartial pressure of the gas to be dissolved in the chamber with the moldis higher than that in the chamber with the reservoir for the melt.Thus, the solubility of the gas, which depends on its partial pressure,may be equal in the melt, as well as in the solidifying metal, and thetotal gas pressure in both chambers may be chosen in accordance with therequirements of the casting process, i.e., to be equal in both chambers,or to be increased from the side of the chamber with the reservoir forthe melt, so that the melt may be conveyed to the mould.

For a better understanding of the invention, reference should be made tothe accompanying drawings, in which preferred devices are shown, suchdevices permitting the practice of the process of the invention; in thedrawings:

FIG. 1 shows a first embodiment of apparatus, in which the melt isconveyed under the action of gas pressure; and

FIG. 2 shows a second embodiment of apparatus, in which the melt isconveyed gravitationally.

Turning now to FIG. 1, the reservoir for the melt l is placed in ahermetically closed and heat-insulated or heated chamber 2, and isconnected by means of a delivery pipe 3 to the mould 4, which is closedin another hermetic chamber 5. In order to control the connectionbetween the two chambers, a valve 6 and a barrier 7 are provided on thedelivery pipe 3 along the path of the metal, which can be controlled bymeans of familiar devices, i.e., selectively to close and open thedelivery pipe while the process takes place.

Two reservoirs 8 and 9 contain under pressure the gas being dissolvedmixed with an inert gas at different and suitably chosen concentrations,while a circulation-regenerative system 10 is provided for purificationand returning to these reservoirs the gases that escape from thehermetic chambers with the reservoir for the melt and with the mould.The capacity and the pressure of the gas flows are controlled by thevalves 12 to 17.

According to the present invention, the process is carried out in theapparatus of F IG. 1 in the following way.

While the barrier 7 is closed and the valve 6 is open, the chamber 2with the reservoir for the melt l is filled by opening the valve 12 topermit a gas mixture from the reservoir 8 to flow into a tube 11immersed in the melt for treating it. It is important that the deliveryof the gas mixture should be done slowly and should take place throughthe melt, by means of the pipe 11 or through a porous wall at the bottomof the crucible, thus ensuring a good mixing of the gas with the melt.At the same time, a gas mixture from reservoir 9 is let in through thevalve 13 into the chamber 5 with the mould 4. The pressures in bothchambers 2 and 5 are equal during this preparatory stage of the process,so that by opening the barrier 7 no moving of the melt is provoked.

By closing the valve 6 and increasing the pressure in chamber 2, themelt is conveyed along the delivery pipe 3 to the mould 4 and fills it.If the concentration of the active gas in the reservoir 9, respectivelyin the chamber 5 and the mould 4, is considerably higher than that inthe reservoir 8 and in the chamber 2, it is not possible, because of theshort time of filling the mould, to enrich considerably the molten metalwith gas; but the whole crystallization process in the mould, whichbegins immediately after filling of the said mould with melt, takesplace at a high partial pressure of the active gas, i.e., the gasalready dissolved in the melt 1 cannot be separated from thesolidifying-melt and remains dissolved in the said melt. By making thepressure in both chambers equal, which is done after filling the mould,the superfluous melt from the delivery pipe returns in the reservoir forthe melt, and the barrier 7 may be closed. It will be easy, if needed,to increase additionally the pressure of the active gas in chamber 5during the period till the crystallization of the casting is completed.

The casting is removed from the mould 4 after the active gas fromchamber'S has been sucked through valve 17 in thecirculation-regenerative system 10, in order to be returned in reservoir9. After the removal of the filled mould and the placing of an emptymould and restoring the initial condition of the apparatus, the castingprocess may be repeated. During the whole time the gas atmosphere inchamber 2 with the reservoir for the melt 1 is not exchanged, while thepressure varies only within narrow limits, so that the melt can be movedtowards the mould or back. In accordance with this, valve 16 is operatedfor sucking the gas from chamber 2 only after the molten metal inreservoir 1 has been totally drained.

According to another quite analogic execution, as shown in FIG. 2, theapparatus may operate while the melt is conveyed to the mouldgravitationally. As shown in FIG. 2, the apparatus has the same basicelements as the apparatus of FIG. 1, and designated by the samereference characters. In the apparatus of FIG. 2, however, the reservoirfor the melt is disposed higher than the mould 4. The melt flow may becontrolled by a known stopper device 18, which is operated from outsidethe reservoir for the melt, and opens or closes the pouring hole at thebottom of said reservoir at will.

What is claimed is:

l. A method for the production of castings from alloys of I metals andgases, which comprises disposing a reservoir for a melt of metal in afirst hermetically closed chamber, disposing a mould in a secondhermetically closed chamber, subjecting both chambers to the pressure ofan atmosphere composed of the gas to be dissolved in the molten metaland some other gas which is inert to the metal, feeding molten metalfrom the reservoir into the mould, and controlling the proportions ofsaid gases so that the partial pressure of the gas to be dissolved inthe second chamber is higher than that in the first chamber, andmaintaining such condition until the casting completely solidifies.

2. A method for production of castings from alloys of metals and gasesaccording to claim 1, wherein the gas pressure in the second chamber isabruptly increased after the mould has been filled with molten metal.

3. A method according to claim 1, wherein the mould is disposed abovethe reservoir, and causing a charge of metal to be fed upwardly from thereservoir to the mould by increasing the gas pressure in the firstchamber with respect to that in the second chamber.

4. A method according to claim 1, wherein the mould is disposed belowthe reservoir, and comprising feeding a charge of metal from thereservoir to the mould by gravity.

2. A method for production of castings from alloys of metals and gases according to claim 1, wherein the gas pressure in the second chamber is abruptly increased after the mould has been filled with molten metal.
 3. A method according to claim 1, wherein the mould is disposed above the reservoir, and causing a charge of metal to be fed upwardly from the reservoir to the mould by increasing the gas pressure in the first chamber with respect to that in the second chamber.
 4. A method according to claim 1, wherein the mould is disposed below the reservoir, and comprising feeding a charge of metal from the reservoir to the mould by gravity. 